Whole blood is a tissue with two components: the blood cells (red corpuscles, leukocytes and platelets), and plasma, a pale yellow liquid in which the blood cells are in suspension.
At the present time, patients are given transfusions only of the blood components necessary for their condition. For example, only platelet concentrates are transfused to patients suffering from thrombocytopenia, that is to say those whose platelet content in the blood is reduced.
Blood components are normally separated by two types of centrifugation. “Soft” centrifugation of the whole blood results in separation into two layers: a bottom layer with a high red corpuscle content known as a red corpuscle concentrate (RCC); and a top layer containing the plasma, platelets and leukocytes, referred to as a platelet-rich plasma (PRP). “Hard” centrifugation results in a separation into three layers: a bottom layer of RCC; a top layer of plasma with a low platelet content; and an intermediate layer formed essentially of leukocytes and platelets, referred to as a leukocyte-platelet layer or buffy coat. The platelet concentrate (PC) is obtained by centrifugation of the PRP or the buffy coat.
The presence of leukocytes in blood components intended for transfusion has very significant undesirable effects. Leukocytes increase the risks of immune rejection such as GVHD (Graft Versus Host Disease: rejection of the graft by the host) and assist in the transmission of infectious agents. Leukocytes also negatively affect the preservation of platelets. Therefore, it is desirable to remove leukocytes from blood or blood components. Filtration units with a medium for deleukocytation of the whole blood and/or each of the blood components have been developed. However, the majority of these media retain the not only leukocytes but also the platelets so that they do not make it possible to obtain a platelet filtrate product free from leukocytes.
To allow the selective elimination of the leukocytes and the passage of platelets, several chemical and/or physical treatments of known filtering media have been proposed.
For example, it has been envisaged treating the filtering medium by coating or radiation grafting of various chemical substances may limit the adhesion of the platelets to the filtering medium. These treatments have the drawback of using organic reagents which may be found in the leukodepleted blood or blood component.
In addition, it has been envisaged, for example in WO-93/04763, to treat the filtration medium by gas plasma so as to reduce the retention of the platelets. However, to be effective, this type of treatment may require operating conditions, particularly in terms of time, which are constraining.